range-top

Returns the value of the range-top property of
a value-axis. The value
may be set at creation time by passing
the range-top initarg, or any
time later by calling (setf range-top).

A value to use for the high end of a value-axis in a chart-widget. The value should be a real
number, or else nil to have the value
computed automatically. The default value
is nil.

When the value is a number, it should typically be greater than or
equal to the largest data value that is being charted, or at least
greater than the largest value that you're interested in viewing at
the moment.

When the value is computed automatically, a relatively "round" number
is chosen that is equal to or somewhat greater than the largest data
value. If set-chart-value is
later called to add a value that is greater than the current
automatically computed range top, then a new range top will be
computed to encompass the new value.

To force a new range top to be computed (when the value of this
property is nil), call update-chart-widget. This may be useful to
recompute the range after set-chart-value has been used to modify values
so that the data range is smaller, or if something has changed to
cause the widget's chart-value-returner function to return a
different range of values.